What's so special about our Dynaco upgrade boards?
The object of our upgrade boards is to provide a dropin replacement for the original boards that would result in a perceptible improvement in sound quality and overall performance, use readily available tubes, and, in keeping with the original Dynaco philosophy, sell for a reasonable price. In other words, using our board, you get improved performance just by installing the board, there aren't any additional controls to bother with, or shoehorning in more parts in the amp.
There's certainly other "dropin" boards, but most of them use 6GH8 or a similar triode/pentode which are a step back in performance compared to the original 7199, and no better than a 6AN8. Basically, you're getting improved quality parts, but no better performance otherwise than the original board if it had better parts to begin with...actually, on the average, 6GH8 have worse noise performance than 7199's do. Our board with either 6AU6/EF94 (ST70) or a cascoded 12AU7 (Mk3/Mk2 board), gives improved performance in this respect, and most people agree it sounds better, too. The ST-70 board also cuts DC grid circuit resistance of the EL34's by about 2/3rds, which reduces or eliminates pesky bias-drift problems.
Our board's a great choice if you really want to learn more about how your amplifier operates, too. You see,unlike many other modifications, you are not totally locked in to only certain components, nor are you stuck with unchangeable circuit values which limit the versatility of your amplifier and further modifications. There's no "big secrets",you don't need permission from a "guru" to change or tweak it, the 20 page manual has instructions for about every change you could imagine making. Instructions are included for triode connecting the output tubes, which will give you a taste of hi-end triode-itis for the cost of 4 resistors, about $1.
So, you've got a choice..you can just plug in & play, or you can do your own experimenting if you'd like to, learn a lot and become your own neighborhood Dynaco guru. And you won't break the bank doing it, either.
The stock board parts kit includes metal film resistors, polypropylene & polystyrene capacitors, and gold plated tube sockets..which do just fine..but if you like you can modify many component values and try different or exotic parts and tweak to your heart's content. The boards will adapt to output tubes which need very low drive circuit impedance/ DC grid resistance like 8417's- or may be modified to whip out enough voltage to drive 6B4's!! (even 300B's might work..we haven't tried it yet..).
The board sounds fine even with the off the shelf, current production tubes, and special grading and matching is not absolutely necessary. It is a good example of what can be done with the original type of circuit with improved components, and makes a good case for the virtues of simplicity and short signal path in audio design. PC1 boards emulate the simple but highly effective (due to the short signal path and single gain stage) original Dynaco circuit, but with lower hum, noise, distortion and a wider voltage swing across heavier loads than a 7199,6GH8,6BL8/ECF80, 6U8/ECF82 or 6AN8 are capable of.
The manual includes information on adapting the amplifier to different output & board tubes, adjusting resistor & capacitor values if desired, plus a comprehensive Troubleshooting Guide.
The Mark 4/3/2 board uses a cascoded triode front-end, which gives "pentode gain with triode noise" and allows the use of a wide variety of possible tubes with pinouts same as 12AU7, by simply changing 2 resistors on the board.
The Mark 3/2 manual also includes a special section on Mark 2's.
The ST-70 board uses an 6AU6/EF94 (or compatible tube) front-end..don't be scared of this pentode, like Sam I Am, you'll be pleasantly surprised. There's a plethora (at least a dozen types) of tubes that are cheap and pin-compatible with 6AU6 if you want to try some bargain tube rolling! We also offer our "classic" EF-86 version.
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